1. Field of the Invention
The present invention relates to prostheses and, in particular, to ocular prostheses for replacing, for example, diseased or damaged corneas or portions of corneas.
2. Description of Related Art
Several attempts have been made to provide prostheses for the replacement of diseased or injured corneas. One such prosthesis is described in U.S. Pat. No. 4,865,601, which is intended to lie deep in an intra-lamellar stromal pocket and to be anchored in place by a fibrous ingrowth of tissue into an annular porous skirt of the prosthesis. The implant is anchored beneath the conjunctiva, which is sewn together in a flap over the eye, allowing for support for the six to eight weeks needed for the implant to root. The conjunctiva flaps open gradually between the sixth and eighth week during which time sight is gradually regained.
The prosthesis used in U.S. Pat. No. 4,865,601 includes an optical element made from polyurethane, which is surrounded by a porous annular skirt made from polytetrafluoroethylene ("Goretex"). The porous skirt is intended to permit the fibrous ingrowth of tissue. The optical element is bonded to the annular skirt by introducing a polymerization mixture into the area where the optical element and skirt overlap, to bond the two different materials together.
A problem in the art of prostheses for implantation in the eye involves breach of the barrier which protects the internal parts of the eye, thereby allowing for invasion by external pathogens and resultant infections. Previous attempts to alleviate this problem have used prostheses, or parts thereof, made of a porous material into which eye tissue can grow to create a barrier. Such a barrier, however, is dependent on sufficient ingrowth of tissue into the porous material and can take from weeks to months to develop.
Protective measures, such as the surgical creation of the conjunctival flap discussed above, must be taken during the corneal fibroblast ingrowth in the pores for two main reasons: (1) to protect the eye from external pathogens during this period, and (2) to prevent the epithelial downgrowth of the conjunctival cells in between the wound edges, by directing them on top of the inert synthetic material of the prosthesis where they have no chance to be anchored and, therefore, no chance of reaching the wound before the healing process performed by the ingrowth of the corneal fibroblast in the pores of the peripheral prosthesis occurs. In the case of conjunctival flaps, the patient does not regain vision until at least six to eight weeks after surgery.
Another related problem with the background art relating to ocular protheses is that specific surgical procedures, such as the creation and sewing together of the conjunctival flaps, must be performed after a broad dissection of the conjunctiva which will not feed into the inert material of the prosthesis.
Accordingly, it is an object of the present invention to provide a corneal implant which enables the patient to see immediately after surgery.
Another object is to provide an ocular prosthesis which permits the use of eye tissue, such as the conjunctiva, as a means of immediately anchoring the prosthesis to the eye during surgery.
Another object is to provide an ocular prosthesis wherein eye tissue, such as conjunctiva tissue, may be actively directed to an anatomical synthetic for its insertion in a way to prevent epithelial down growth and to create an anatomical and clearly limited barrier against any external pathogens.
A further object is to provide a simpler surgical procedure for implanting an artificial cornea, resembling that which is used for corneal transplants.